1. Field of Invention
The present invention relates to a method for suppressing impulse noise. More particularly, the present invention relates to a method for comparing the energy sums of a plurality of samples in a sample stream with thresholds to detect and suppress impulse noise and the device thereof, and the method is applicable to various digital communication receivers.
2. Description of Related Art
Impulse noise is composed of one or multiple pulses having large oscillation amplitude (or energy) and short period. Impulse noises may occur in, for example, electrical wire spool apparatus, central heater thermostat, lightning switch, or ignition system. These impulse noises may interrupt the decision-making regarding transmission symbols of the communication system and may reduce the performance of the entire communication system. For example, in digital terrestrial TV system, Coded Orthogonal Frequency Division Multiplexing (COFDM) is adopted in the European Digital Video Broadcasting-Terrestrial (DVB-T) standard as the transmission modulation technology of digital bit stream and which is prone to interruption of impulse noises.
Accordingly, suppressing impulse noise at the receiver portion has become an important method for improving system performance. In European Patent No. 1,043,874, the clipping level of an analog-to-digital converter (ADC) is used as the threshold. When the data level of a signal converted by the ADC is higher than the positive clipping level or is lower than the negative clipping level, it is determined that the data has been interrupted by impulse noise and is to be replaced with a digital value to be output. Here, the digital value may be 0 or the long-term average of the signal.
In European Patent No. 1,180,851, the threshold is generated dynamically by a threshold generator according to a digital stream and is provided to a comparator. The comparator compares the threshold and a digital data to determine whether the digital data is interrupted by impulse noise and is to be replaced with a digital value. Here, the digital value may be 0 or the moving average of the signal.
Moreover, in European Patent No. 1,309,095, several consecutive digital data in the signal are compared with the threshold by a delay chain, and it is determined that whether these digital data are interrupted by impulse noises and are to be replaced with digital values according to the comparison results. For example, when the values of more than 4 digital data in eight digital data are greater than the threshold, which means the signal has started to be interrupted by impulse noise, then it is started to replace the digital data with a digital value to output until at the same time the value of at most one digital data in the eight digital data is smaller than the threshold.